This invention relates to electronic imaging systems, and more particularly to a wide angle lens system which compensates a solid state electronic image sensor having a long exit pupil distance.
In the construct of electronic video imaging systems, it is desirable to be able to effectively focus incoming light received from a target onto the imaging substrate of an electronic image sensor, such as a Charge Coupled Device (CCD).
Certain diagnostic instruments such as borescopes and endoscopes used for industrial and medical applications, respectively, include optical focusing systems having a relatively short exit pupil distance (E.P.D.) on the order of approximately 2 to 6 mm which produces a relatively wide field of view (e.g., 50xc2x0-70xc2x0). Conversely, miniature electronic image imagers for video camcorders, hand-held photographic digital cameras, and the like which are mass manufactured by the Eastman Kodak Company and the Sony Corporation, among others, are typically designed with a long E.P.D. of about 20 to 30 mm, producing a comparatively narrow field of view of about 10xc2x0-20xc2x0.
Emphasis on compactness of design is especially important to resolving issues such as comfort for the patient in the case of medical endoscopic devices, and ease in allowing the instrument to traverse a narrow cavity, such as a pressure vessel, in the case of industrial borescopes. Therefore, considerable interest is maintained in reducing the size of the electronic imager. Size reductions in some, however, accentuate the mismatch between the electronic imager and the focusing optics of the device in that the picture brightness is increasingly attenuated as a function of the radial distance from the center of the field of view. The angle of the light rays propagating from the focusing lens to the microlens array of the imager does not fully strike the corresponding pixels on the CCD. This attenuation causes undesired flicker in the processed video image. solid state image sensors, such as CCDs or further including CMOS-type imagers, can be designed with shorter EPDs to compensate for the above noted mismatches, such devices are not commonly manufactured, and therefore would significantly increase associated costs.
It is therefore a primary object of the present invention to improve the state of the art of electronic imaging systems.
It is a further object of the present invention to alleviate potential mismatches between solid state imagers having long exit pupil distances and optical devices such as borescopes and endoscopes, that require a wider field of view.
Therefore, and according to a preferred aspect of the invention, there is described an imaging assembly comprising:
a miniature electronic image sensor including an imaging substrate having a plurality of pixels and a microlens array aligned with corresponding pixels on said imaging substrate; and
focusing optics for focusing an optical image of a target onto said imaging substrate including at least one adaptive lens element, in which said focusing optics have a first exit pupil distance defining a first field of view and said electronic image sensor has a second exit pupil distance defining a second field of view, the first exit pupil distance being different from the second exit pupil distance, and in which said adaptive lens element directs light onto said imaging substrate through said microlens array while permitting the imaging assembly to maintain the first field of view.
Preferably, the adaptive lens element(s) are existing lenses within the focusing optics having adequate power to cause light rays in the imaging plane to enter the lenslet array at approximately the same angle as the rays which would have entered for focusing optics of a system set for an image sensor having a longer exit pupil distance (EPD) than that of the focusing optics.
According to another preferred aspect of the present invention, there is disclosed an intraoral dental camera including:
a housing and a camera head disposed at a distal end of said housing, and in which the camera head includes an imaging assembly comprising:
a miniature electronic image sensor having a plurality of pixels arranged on an imaging substrate and an array of microlenses aligned with corresponding pixels on said imaging substrate; and
focusing optics for focusing an optical image of a target onto said imaging substrate, said focusing optics including at least one adaptive lens element, wherein said focusing optics has a first exit pupil distance defining a first field of view and the image sensor has a second exit pupil distance defining a second field of view, wherein said at least one adaptive lens element directs light to the microlens array from a target while maintaining the field of view of the focusing optics.
Though preferably the camera head imaging assembly is configured to configure a long EPD image sensor with focusing optics having a smaller EPD (a wider field of view), an adaptive lens element can similarly be configured for use with an image sensor having a smaller EPD than that of the focusing optics.
An advantage of the present invention is that miniature electronic image sensors with long EPDs, such as those which are more commonly mass produced for use in video camcorders, hand-held photographic digicams, and the like, can more easily be incorporated into endoscopic and borescopic devices, such as intraoral dental cameras, which require a substantially wider wide field of view than the former devices.
These and other objects, features and advantages will become apparent from the following Detailed Description when read in conjunction with the accompanying drawings.